1. Field of the Invention
This invention relates to the manufacture of electronic devices such as integrated circuits. Particularly, this invention relates to improved semiconductor substrate materials, such as silicon wafers, used in the manufacture of integrated circuit devices. Specifically, this invention is directed to semiconductor substrate materials having a region extending from the device formation surface into the bulk substrate substantially free of microdefects and with reduced oxygen concentration, and possessing enhanced ability for gettering deleterious impurities, contaminants and defects during device manufacture away from the region of device formation.
In the manufacture of integrated circuit devices on silicon wafers, the presence of and introduction of defects, contaminants and impurities on and near the device formation surface of the wafer creates excessive current leakages which greatly affect the yield of usable devices obtained. The art has recognized that the deleterious defects, contaminants and impurities can be to some extent relocated to non-harmful regions in the substrate material away from the device formation region. The methods and processes for diffusing and trapping the defects, contaminants and impurities away from the active device region both prior to and during device formation are termed gettering in the electronics industry and art. It is known in the art that precipitation of oxygen in substrate materials provides lattice strain which gives rise to dislocation loops and stacking faults that provide gettering sites.
Additionally, the art recognizes the desirability of depleting oxygen contained in the substrate material from a region of the bulk substrate at the surface where devices are formed as an aid in reducing defects which adversely effect the devices. The oxygen depletion in this region is referred to as denuding in the electronics industry and art.
2. Description of the Prior Art
Several techniques and processes for gettering in semiconductor materials to improve device yields have been disclosed in the art. Known gettering techniques and processes for semiconductor materials can be generally classified as based on external or internal means.
In copending U.S. application Ser. No. 466,249 filed Feb. 14, 1983 now U.S. Pat. No. 4,608,095, an improved silicon substrate having enhanced gettering ability for defects, contaminants and impurities is described and claimed. The improved substrate utilizes a layer of polysilicon on the backside of a bulk silicon substrate to provide external gettering means. The polysilicon layer also enhances the oxygen precipitation in the substrate which provides internal gettering ability. The combination of external polysilicon and internal oxygen gettering offers many advantages in the newer lower temperature device fabrication processes. The full teachings of this copending application for improved silicon substrates having a polysilicon layer formed on the backside are hereby incorporated herein.
Recently, UK patent application No. 2080780 was published which is directed to a multistep process wherein silicon slices are heated above 1100.degree. C. for 4 to 16 hours to diffuse oxygen from the surface areas and form a denuded zone and then heated at 650.degree.-850.degree. C. for 14 to 16 hours to nucleate defects for providing gettering sites within the center portion of the bulk substrate. Also, European Patent Application No. 0066461 was recently published which is directed to a multistep process wherein silicon slices are first heated at a temperature from 1000.degree.-1200.degree. C. to remove oxygen from the front surface region and form a denuded zone, then heated at a temperature from 600.degree.-1000.degree. C. to form a nucleus of crystal defects below the oxygen reduced region and then heated at a temperature from 1050.degree.-1150.degree. C. to form only stacking faults beneath the oxygen reduced region for providing gettering sites. Another European Patent Application No. 0030457 discloses treating a wafer at 950.degree. to 1300.degree. C. in a non-oxidizing atmosphere to diffuse oxygen from the surface region and form a denuded zone and then heating at 600.degree. to 800.degree. C. to create a high density of defects in the interior of the wafer to provide gettering sites for impurities. In Japanese Kokai Pat. No. 57[1982]-211737 semiconductor substrates are prepared by first growing a 0.5-2.5 micron thick monocrystalline silicon layer on the back surface of the substrate at a temperature above 970.degree. C. and then thermo oxidizing the substrate at about 1140.degree. C. in a wet oxygen environment. This treatment is said to reduce surface defects on the front surface of the wafer.
With any gettering means, the active region of the substrate material where the devices are formed must be free of gettering sites. Thus, a zone about 5-75 microns and preferably about 10-20 microns in depth from the device surface of the wafer which is denuded of gettering sites must be created to prevent device yield loss from defect interference. The oxygen concentration in a substrate material can be reduced near the surface through outward diffusion at the process thermal conditions employed in device manufacture when the process temperatures are sufficiently high to favor out diffusion of oxygen from the substrate rather than precipitation of the oxygen within the substrate material.
With the rapidly advancing device manufacturing technology and particularly with respect to complex and lengthy processing steps, decreased processing temperatures and increased circuit density and total circuit size on a wafer, it has become apparent that improvements are needed in the perfection of the device surface region of substrates and in the gettering capabilities of the bulk substrates to cope with the increased requirements and provide gettering throughout the device processing steps in order to achieve an acceptable yield of good devices per wafer.